Coated nanotube surface signal probe and method of attaching nanotube to probe holder

ABSTRACT

The present invention realizes a probe with a high resolution, high rigidity and high bending elasticity which can be used in a scanning probe microscope and makes it possible to pick up images of surface atoms with a high resolution. Also, a high-precision input-output probe which can be used in high-density magnetic information processing devices is also realized.  
     In order to accomplish the object, the electronic device surface signal operating probe of the present invention is constructed from a nanotube  24 , a holder  2   a  which holds this nanotube  24 , and a fastening means which fastens the base end portion  24   b  of the nanotube  24  to the surface of the holder so that the tip end portion  24   a  of the nanotube  24  protrudes; and the tip end portion  24   a  of the nanotube  24  is used as a probe needle. Furthermore, as one example of the fastening means, a coating film  29  which covers the base end portion  24   b  of the nanotube  24  is formed. If a coating film  30  is also formed on an intermediate portion  24   c  on the root side of the tip end portion, the strength of the probe needle and the resolution are further increased. As another example of the fastening means, the base end portion  24   b  of the nanotube  24  is fusion-welded to the holder surface. All or part of the base end portion  24   b  forms a fusion-welded part so that the nanotube  24  is firmly fastened to the holder.  
     A common nanotube such as a carbon nanotube (CNT), BCN type nanotube or BN type nanotube, etc., can be used as the above-described nanotube. Since nanotubes have a small tip end curvature radius, signals can be operated at a high resolution. Furthermore, since nanotubes have a high rigidity and bending elasticity, they are extremely resistant to damage and have a long useful life. Moreover, since the raw materials are inexpensive, high-performance probes can be inexpensively obtained. Furthermore, such probes can be used as probe needles in scanning tunnel microscopes or atomic force microscopes, or as input-output probes in place of magnetic heads in magnetic disk drives.

DESCRIPTION

[0001] 1. Technical Field

[0002] The present invention relates to a surface signal operating probefor an electronic device which uses a nanotube such as a carbonnanotube, BCN type nanotube, BN type nanotube, etc. as a probe needle.More particularly, the present invention relates to an electronic devicesurface signal operating probe which realizes a concrete method forfastening a nanotube to a holder, and which can be used as the probeneedle of a scanning probe microscope that picks up images of surfacesof samples by detecting physical or chemical actions on the samplesurfaces or as the input-output probe needle of a magnetic disk drive;and it further relates to a method for manufacturing such a probe.

[0003] 2. Background Art

[0004] Electron microscopes have been available in the past asmicroscopes for observing sample surfaces at a high magnification.However, since an electron beam will only travel through a vacuum, suchmicroscopes have suffered from various problems in terms of experimentaltechniques. In recent years, however, a microscopic technique known as a“scanning probe microscope” has been developed which makes it possibleto observe surfaces at the atomic level even in the atmosphere. In thismicroscope, when the probe needle at the tip end of the probe is causedto approach very close to the sample surface at an atomic size, physicaland chemical actions of the individual atoms of the sample can bedetected, and an image of the sample surface can be developed fromdetection signals while the probe needle is scanned over the surface.

[0005] The first microscope of this type is a scanning tunnel microscope(also abbreviated to “STM”). Here, when a sharp probe needle located atthe tip end is caused to approach to a distance at which the attractiveforce from the sample surface can be sensed, e.g., approximately 1 nm(attractive force region), a tunnel current flows between the atoms ofthe sample and the probe needle. Since there are indentations andprojections on the sample surface at the atomic level, the probe needleis scanned across the sample surface while being caused to approach andrecede from the sample surface so that the tunnel current remainsconstant. Since the approaching and receding signals from the probeneedle correspond to the indentations and projections in the samplesurface, this device can pick up an image of the sample surface at theatomic level. A weak point of this device is that the tip end of theprobe needle made of a conductive material must be sharpened in order toincrease the resolution.

[0006] The probe needle of an STM is formed by subjecting a wirematerial of platinum, platinum-iridium or tungsten, etc., to asharpening treatment. Mechanical polishing methods and electrolyticpolishing methods are used for this sharpening treatment. For example,in the case of platinum-iridium, a sharp sectional surface can beobtained merely by cutting the wire material with the nippers of a tool.However, not only is the reproducibility inaccurate, but the curvatureradius of the tip end is large, i.e., around 100 nm, and such acurvature radius is inadequate for obtaining sharp atomic images of asample surface with indentations and projections.

[0007] Electrolytic polishing is utilized for tungsten probe needles.FIG. 25 is a schematic diagram of an electrolytic polishing apparatus. Aplatinum electrode 80 and a tungsten electrode 81, which constitutes theprobe needle, are connected to an AC power supply 82 and are suspendedin an aqueous solution of sodium nitrite 83. As current flows, thetungsten electrode 81 is gradually electrolyzed in the solution, so thatthe tip end of this electrode is finished into the form of a needle.When polishing is completed, the tip end is removed from the liquidsurface; as a result, a tungsten probe needle 84 of the type shown inFIG. 26 is completed. However, even in the case of this tungsten probeneedle, the curvature radius of the tip end is about 100 nm, andindentations and projects formed by a few atoms or more cannot besharply imaged.

[0008] The next-developed scanning type probe microscope is the atomicforce microscope (abbreviated as “AFM”). In the case of an STM, theprobe needle and sample must as a rule be conductors in order to causethe flow of the tunnel current. Accordingly, the AFM is to observe thesurfaces of non-conductive substances. In the case of this device, acantilever 85 of the type shown in FIG. 27 is used. The rear end of thiscantilever 85 is fastened to a substrate 86, and a pyramid-form probeneedle 87 is formed on the front end of the cantilever 85. A point part88 is formed on the tip end of the probe needle by a sharpeningtreatment. The substrate 86 is mounted on a scanning driving part. Whenthe point part is caused to approach the sample surface to a distance ofapproximately 0.3 nm from the sample surface, the point part receives arepulsive force from the atoms of the sample. When the probe needle isscanned along the sample surface in this state, the probe needle 87 iscaused to move upward and downward by the above-described repulsiveforce in accordance with the indentations and projections of thesurface. The cantilever 85 then bends in response to this in the mannerof a “lever”. This bending is detected by the deviation in the angle ofreflection of a laser beam directed onto the back surface of thecantilever, so that an image of the surface is developed.

[0009]FIG. 28 is a diagram of the process used to manufacture theabove-described probe needle by means of a semiconductor planartechnique. An oxide film 90 is formed on both surfaces of a siliconwafer 89, and a recess 91 is formed in one portion of this assembly bylithography and etching. This portion is also covered by an oxide film92. The oxide films 90 and 92 are converted into Si₃N₄ films 93 by anitrogen treatment; then, the entire undersurface and a portion of theupper surface are etched so that a cut part 94 is formed. Meanwhile, alarge recess 96 is formed in a glass 95, and this is anodically joinedto the surface of the Si₃N₄ film. Afterward, the glass part 97 is cut,and the silicon part 98 is removed by etching. Then, the desired probeneedle is finished by forming a metal film 99 used for laser reflection.Specifically, the cantilever 85, substrate 86, probe needle 87 and pointpart 88 are completed.

[0010] This planar technique is suited for mass production; however, theextent to which the point part 88 can be sharpened is a problem. In thefinal analysis, it is necessary either to sharply etch the tip end ofthe recess 91, or to sharpen the tip end of the probe needle 87 byetching. However, even in the case of such etching treatments, it hasbeen difficult to reduce the curvature radius of the tip end of thepoint part 88 to a value smaller than 10 nm. The indentations andprojections on the sample surface are at the atomic level, and it isnecessary to reduce the curvature radius of the tip end of the pointpart 88 to a value of 10 nm or less in order to obtain sharp images ofthese indentations and projections. However, it has been impossible toachieve such a reduction in the curvature radius using this technique.

[0011] If artificial polishing and planar techniques are useless, thequestion of what to use for the probe needle, which is the decidingelement of the probe, becomes an important problem. One approach is theuse of whiskers (whisker crystals). Zinc oxide whiskers have actuallybeen utilized as probe needles. Whisker probe needles have a smaller tipend angle and tip end curvature than pyramid needles produced by planartechniques, and therefore produce sharper images. However, whiskermanufacturing methods have not been established, and the manufacture ofconductive whiskers for STM use has not yet been tried. Furthermore,whiskers with the desired cross-sectional diameter of 10 nm or less havenot yet been obtained.

[0012] Furthermore, such probe needles have suffered from many otherproblems: e.g., such probe needles are easily destroyed by strongcontact with the sample surface, and such needles quickly become wornunder ordinary use conditions, so that use becomes impossible.

[0013] In recent years, therefore, the idea of using carbon nanotubes asprobe needles has appeared. Since carbon nanotubes are conductive, theycan be used in both AFM and STM. A carbon nanotube probe needle has beenproposed as a high-resolution probe for imaging biological systems in J.Am. Chem. Soc., Vol. 120 (1998), p. 603. However, the most importantpoints, i.e., the question of how to collect only carbon nanotubes froma carbon mixture, and the question of how to fasten carbon nanotubes toa holder, remain completely unsolved. In this reference as well, the useof an assembly in which a carbon nanotube is attached to a holder bymeans of inter-molecular force is mentioned only in passing.

[0014] Furthermore, besides carbon nanotubes, BCN type nanotubes and BNtype nanotubes have also been developed as nanotubes. However methods ofutilizing such nanotubes have remained completely in the realm of theunknown.

[0015] On a different subject, memory devices have evolved from floppydisk drives to hard disk drives, and further to high-density diskdrives, as the memory capacity of computers has increased in recentyears. As information is packed into smaller spaces at higher densities,the size per bit of information decreases; accordingly, a finer probeneedle is also required for input-output. In conventional magnet headdevices, it is impossible to reduce the size of the probe needle beyonda certain fixed value, so that there are limits to the trend towardhigher density.

[0016] As described above, systematic conventional techniques forsharpening probe needles are electrolytic polishing of metal wirematerials and lithography and etching treatments of semiconductors. Inthe case of these treatments, however, the tip end curvature radius ofthe probe needle can only be sharpened to about 100 nm; accordingly, itis very difficult to obtain sharp images of indentations and projectionsformed by a few atoms or more on the sample surface. Furthermore, thedegree of sharpness obtained by mechanically cutting metal wirematerials with a tool such as nippers, etc. is also insufficient tocapture sharp images of indentations and projections. The use ofwhiskers is still an uncertain technique, and the use of nanotube probeneedles such as carbon nanotubes, etc. has been a task for the future.Furthermore, conventional magnetic head devices have also approachedtheir limit in terms of size.

[0017] Accordingly, the object of the present invention is to providethe utilization of nanotubes with a small tip end curvature radius assurface signal operating probe needles and further to establish aconcrete structure for probes using nanotube probe needles, and a methodfor manufacturing the same. The present invention shows that suchnanotube probe needles are not easily destroyed even when they contactatomic-level projections during probe needle scanning, that such probeneedles can be firmly fastened to the holder so that the probe needlewill not come loose from the holder during such scanning, and that suchprobe needles can be inexpensively mass-produced. Furthermore, thepresent invention shows that samples that could not be observed withhigh resolution in the past can be clearly observed using the nanotubeprobe needles thus manufactured.

DISCLOSURE OF INVENTION

[0018] The present invention is to accomplish the above-describedobject. The surface signal operating probe for electronic devices of thepresent invention is characterized in that the probe comprises ananotube, a holder which holds the nanotube, and a fastening means whichfastens the base end portion of the nanotube to the surface of theholder so that the tip end portion of the nanotube protrudes; andsurface signals are operated by the tip end portion of the nanotube thatis used as a probe needle.

[0019] The present invention provides a surface signal operating probein which the fastening means is a coating film, and the nanotube isfastened to the holder by covering a specified region of the nanotubeincluding the base end portion by means of the coating film.

[0020] Furthermore, the present invention provides a surface signaloperating probe in which the fastening means is a fused part, and thebase end portion of the nanotube is fusion-welded to the holder by thisfused part.

[0021] The present invention provides a surface signal operating probein which the above-described electronic device is a scanning probemicroscope, and physical and chemical actions on the sample surface aredetected by the nanotube used as a probe needle. Such a scanning probemicroscope includes scanning tunnel microscopes, atomic forcemicroscopes, etc.

[0022] Furthermore, the present invention provides a surface signaloperating probe in which the above-described electronic device is amagnetic information processing device, and magnetic information isinputted onto and outputted from a magnetic recording medium by thenanotube.

[0023] As a method for manufacturing this probe, the present inventionprovides a method for manufacturing an electronic device surface signaloperating probe, and this method comprises a first process in which avoltage is applied across electrodes in an electrophoretic solution inwhich a nanotube that constitutes the probe needled is dispersed, sothat this nanotube is caused to adhere to the electrodes in a protrudingfashion, a second process in which the electrode to which the nanotubeis attached in a protruding fashion and a holder are caused to approachvery closely to each other, and the nanotube is transferred to theholder so that the base end portion of the nanotube adheres to theholder surface in a state in which the tip end portion of the nanotubeis caused to protrude, and a third process in which a specified regionthat includes at least the base end portion of the nanotube adhering tothe holder surface is subjected to a coating treatment so that thenanotube is fastened to the holder by the resulting coating film.

[0024] Furthermore, the present invention provides a method formanufacturing an electronic device surface signal operating probe, andthis method comprises a first process in which a voltage is appliedacross electrodes in an electrophoretic solution in which a nanotubethat constitutes the probe needled is dispersed, so that this nanotubeis caused to adhere to the electrodes in a protruding fashion, a secondprocess in which the electrode to which the nanotube is attached in aprotruding fashion and a holder are caused to approach very closely toeach other, so that the base end portion of the nanotube is caused toadhere to the holder surface in a state in which the tip end portion ofthe nanotube is caused to protrude, and a third process in which anelectric current is caused to flow between the nanotube and the holderso that the base end portion of the nanotube is fused to the holder.

[0025] In addition, the present invention provides a method formanufacturing an electronic device surface signal operating probe, andthis method comprises a first process in which a voltage is appliedacross electrodes in an electrophoretic solution in which a nanotubethat constitutes the probe needled is dispersed, so that this nanotubeis caused to adhere to the electrodes in a protruding fashion, a secondprocess in which the electrode to which the nanotube is attached in aprotruding fashion and a holder are caused to approach very closely toeach other, so that the base end portion of the nanotube is caused toadhere to the holder surface in a state in which the tip end portion ofthe nanotube is caused to protrude, and a third process in which thebase end portion of the nanotube is fused to the holder by irradiationwith an electron beam.

[0026] The present invention provides a surface signal operating probeand a method for manufacturing the same, in which the nanotube is acarbon nanotube, BCN type nanotube or BN type nanotube.

[0027] The term “electronic device” used in the present invention refersto an electronic device that uses a probe for the operation of surfacesignals. For examples, such electronic devices include scanning probemicroscopes; these are devices that image the arrangement of surfaceatoms of a sample using a probe. Furthermore, such electronic devicesalso include magnetic information processing devices; for example,magnetic disk drives such as hard disks, etc., input and output magneticinformation using a magnetic head as a probe. Accordingly, the surfacesignal operating probe of the present invention includes not only casesin which conditions or signals of the opposite surface are detected, butalso cases in which signals are exchanged with the opposite surface.

[0028] Below, the present invention will be described in detail usingmainly a scanning probe microscope as the electronic device of thepresent invention.

[0029] The term “scanning probe microscope” refers to a microscope whichdetects physical and chemical actions from the atoms of the samplesurface by means of the probe needle of a probe, and develops an imageof the sample surface from such detection signals while scanning theprobe needle over the surface of the sample. The probe needle is asensor which detects physical and chemical actions; the probe refers toa device to which the probe needle is attached. The structure of theprobe varies according to the types of physical and chemical actionsdetected, i.e., according to the type of microscope. However, what iscommon to all such probes is a fine probe needle and a probe needleholder to which this probe needle is integrally fastened. In the presentinvention, a nanotube is used as the probe needle.

[0030] Scanning probe microscopes include scanning tunnel microscopes(STM) which detect a tunnel current, atomic force microscopes (AFM)which detect surface indentations and projections using the van derWaals force, leveling force microscopes (LFM) which detect surfacedifferences by means of frictional force, magnetic force microscopes(MFM) which detect magnetic interactions between a magnetic probe needleand magnetic field regions on the sample surface, electric field forcemicroscopes (EFM) which apply a voltage across the sample and probeneedle, and detect the electric field force gradient, and chemical forcemicroscopes (CFM) which image the surface distribution of chemicalfunctional groups, etc. What these microscopes have in common is thatthey all detect characteristic physical or chemical actions by means ofa probe needle, and thus attempt to detect surface information with ahigh resolution at the atomic level.

BRIEF DESCRIPTION OF DRAWINGS

[0031]FIG. 1 is a structural diagram of a scanning tunnel microscope(STM).

[0032]FIG. 2 is a structural diagram of an atomic force microscope(AFM).

[0033]FIG. 3 shows perspective views of various tip end shapes of carbonnanotubes (CNT).

[0034]FIG. 4 is a perspective view illustrating one example of thearrangement of five-member rings and six-member rings in a CNT.

[0035]FIG. 5 is a structural diagram illustrating one example of a DCelectrophoresis method.

[0036]FIG. 6 is a structural diagram illustrating one example of an ACelectrophoresis method.

[0037]FIG. 7 is a schematic diagram showing states of adhesion ofnanotubes to a knife edge.

[0038]FIG. 8 is a computer image of a scanning electron microscope imageof a knife edge with an adhering CNT.

[0039]FIG. 9 is a computer image of a scanning electron microscope imageshowing a CNT prior to the pressing of this CNT by means of a memberwith a sharp tip.

[0040]FIG. 10 is a computer image of a scanning electron microscopeimage showing a CNT immediately after this CNT has been pressed by meansof a member with a sharp tip, wherein the CNT is bent.

[0041]FIG. 11 is a structural diagram of a device used to transfer ananotube to the cantilever of an AFM.

[0042]FIG. 12 is a layout diagram showing the state immediately prior tothe transfer of the nanotube in Embodiment 1.

[0043]FIG. 13 is a layout diagram showing the state immediatelyfollowing the transfer of the nanotube.

[0044]FIG. 14 is a layout diagram showing the formation of a coatingfilm covering the nanotube.

[0045]FIG. 15 is a computer image of a scanning electron microscopeimage of a completed AFM probe.

[0046]FIG. 16 is a computer image of a DNA image picked up by thecompleted AFM probe.

[0047]FIG. 17 is a layout diagram showing a case in which a coating filmis also formed on an intermediate part constituting a region on the baseend side of the tip end portion of the nanotube (as Embodiment 2).

[0048]FIG. 18 is a perspective view which shows the essential parts ofan STM probe as Embodiment 3.

[0049]FIG. 19 is a layout diagram which shows the state immediatelyprior to the fusion-welding of the nanotube in Embodiment 5.

[0050]FIG. 20 is a layout diagram which shows the state immediatelyfollowing the fusion-welding of the nanotube.

[0051]FIG. 21 is a schematic diagram of a completed AFM probe.

[0052]FIG. 22 is a schematic diagram showing the forming of a coatingfilm covering the nanotube in Embodiment 7.

[0053]FIG. 23 is a perspective view which shows essential parts of anSTM probe as Embodiment 8.

[0054]FIG. 24 is a perspective view which shows essential parts of anSTM probe in a case where a coating film is formed on an intermediatepart constituting a region on the base end side of the tip end portionof the nanotube, as Embodiment 9.

[0055]FIG. 25 is a schematic diagram of a conventional electrolyticpolishing apparatus.

[0056]FIG. 26 is a diagram showing the completion of electrolyticpolishing.

[0057]FIG. 27 is a schematic diagram of a conventional AFM probe needle.

[0058]FIG. 28 is a process diagram showing a semiconductor planartechnique for a conventional AFM probe needle.

BEST MODE FOR CARRYING OUT THE INVENTION

[0059] In order to describe the present invention in greater detail, theinvention will be described with reference to the accompanying drawings.

[0060]FIG. 1 is a structural diagram of a scanning tunnel microscope(STM) to which the present invention is applied. The nanotube probeneedle 1 is fastened to a holder 2 a to form a detection probe 2. Themethod of fastening will be described later. This holder 2 a is insertedinto the cut groove 3 a of a holder setting part 3, and is fastened inplace by means of spring pressure so that the holder 2 a can bedetached. A scanning driving part 4 comprises an X piezo-electricelement 4 x, a Y piezo-electric element 4 y and a Z piezoelectricelement 4 z scans the holder setting part 3 by expanding and contractingin the X, Y and Z directions, and thus causes scanning of the nanotubeprobe needle 1 relative to the sample 5. The reference numeral 6 is abias power supply, 7 is a tunnel current detection circuit, 8 is aZ-axis control circuit, 9 is an STM display device, and 10 is an XYscanning circuit.

[0061] The Z axis control circuit controls the nanotube probe needle 1by expansion and contraction in the Z direction so that the tunnelcurrent remains constant at each XY position. This amount of movementcorresponds to the amount of indentation or projection in the Z axisdirection. As the nanotube probe needle 1 is scanned in the X and Ydirections, a surface-atomic image of the sample 5 is displayed by theSTM display device. When the nanotube probe needle 1 is replaced in thepresent invention, the holder 2 a is removed from the holder settingpart 3, and the probe 2 is replaced as a unit.

[0062]FIG. 2 is a structural diagram of an atomic force microscope (AFM)to which the present invention is applied. The nanotube probe needle 1is fastened to a holder 2 a. The holder 2 a is a pyramid-form memberformed on the tip end of a cantilever 2 b. The cross section of thispyramid is a right-angled triangle, and the probe needle 1 is fastenedto the perpendicular surface; accordingly, the probe needle 1 contactsthe sample surface more or less perpendicularly, so that the shape ofthe sample surface can be accurately read. The cantilever 2 b isfastened to a substrate 2 c and fastened in a detachable manner to aholder setting part (not shown). In this configuration, the nanotubeprobe needle 1, holder 2 a, cantilever 2 b and substrate 2 c togetherconstitute the probe 2; when the probe needle is replaced, the entireprobe 2 is replaced. For example, if the conventional pyramid-form probeneedle 87 shown in FIG. 27 is utilized as the holder 2 a, the nanotubeprobe needle can be fastened to this by a method described later. Thesample 5 is driven in the X, Y and Z directions by a scanning drivingpart which is a piezo-electric element. 11 indicates a semiconductorlaser device, 12 indicates a reflective mirror, 13 indicates a two-partsplit light detector, 14 indicates an XYZ scanning circuit, 15 indicatesan AFM display device, and 16 indicates a Z axis detection circuit.

[0063] The sample 5 is caused to approach the nanotube probe needle 1 inthe direction of the Z axis until the sample 5 is in a position where aspecified repulsive force is exerted; and afterward, the scanningdriving part 4 is scanned in the X and Y directions by the scanningcircuit 14 with the Z position in a fixed state. In this case, thecantilever 2 b is caused to bend by the indentations and projections ofthe surface atoms, so that the reflected laser beam LB enters thetwo-part split light detector 13 after undergoing a positionaldisplacement. The amount of displacement in the direction of the Z axisis calculated by the Z axis detection circuit 16 from the difference inthe amounts of light detected by the upper and lower detectors 13 a and13 b, and an image of the surface atoms is displayed by the AFM displaydevice 15 with this amount of displacement as the amount of indentationand projection of the atoms. This device is constructed so that thesample 5 is scanned in the X, Y and Z directions. However, it is alsopossible to scan the probe needle side, i.e., the probe 2, in the X, Yand Z directions. The nanotube probe needle 1 may be caused to vibrateso that it lightly strikes the surface of the sample 5.

[0064] The nanotube probe needle 1 shown in FIGS. 1 and 2 is a nanotubeitself, such as a carbon nanotube, BCN type nanotube or BN typenanotube, etc. Of these various types of nanotubes, the carbon nanotube(also referred to as “CNT” below) was discovered first. In the past,diamond, graphite and amorphous carbon have been known as stableallotropes of carbon. The structures of these allotropes were also instates that were more or less determined by X-ray analysis, etc. In1985, however, fullerene, in which carbon atoms are arranged in the formof a soccer ball, was discovered in a vapor cooled product obtained byirradiating graphite with a high-energy laser, and this compound wasexpressed as C₆₀. In 1991, furthermore, carbon nanotubes, in whichcarbon atoms are arranged in a tubular form, were discovered in acathodic deposit produced by means of a DC arc discharge.

[0065] BCN type nanotubes were synthesized on the basis of the discoveryof such carbon nanotubes. For example, a mixed powder of amorphous boronand graphite is packed into a graphite rod, and is evaporated innitrogen gas. Alternatively, a sintered BN rod is packed into a graphiterod, and is evaporated in helium gas. Furthermore, an arc discharge maybe performed in helium gas with BC₄N used as the anode and graphite usedas the cathode. BCN type nanotubes in which some of the C atoms in acarbon nanotube are replaced by B atoms and N atoms have beensynthesized by these methods, and multi-layer nanotubes in which BNlayers and C layers are laminated in a concentric configuration havebeen synthesized.

[0066] Very recently, furthermore, BN type nanotubes have beensynthesized. These are nanotubes which contain almost no C atoms. Forexample, a carbon nanotube and powdered B₂O₃ are placed in a crucibleand heated in nitrogen gas. As a result, the carbon nanotube can beconverted into a BN type nanotube in which almost all of the C atoms ofthe carbon nanotube are replaced by B atoms and N atoms.

[0067] Accordingly, not only carbon nanotubes, but also generalnanotubes such as BCN type nanotubes or BN type nanotubes, etc., can beused as the nanotubes of the present invention.

[0068] Since these nanotubes have more or less the same substancestructure as carbon nanotubes, carbon nanotubes will be used as anexample in the structural description below.

[0069] Carbon nanotubes (CNT) is a cylindrical carbon substance with aquasi-one-dimensional structure which has a diameter of approximately 1nm to several tens of nanometers, and a length of several microns.Carbon nanotubes of various shapes, as shown in FIG. 3, have beenconfirmed from transmission electron micrographs. In the case of FIG.3(a), the tip end is closed by a polyhedron, while in the case of FIG.3(b), the tip end is open. In the case of FIG. 3(c), the tip end isclosed by a conical shape, while in the case of FIG. 3(c), the tip endis closed by a beak shape. In addition, half-donut type nanotubes arealso known to exist.

[0070] It is known that the atomic arrangement of a carbon nanotube is acylinder which has a helical structure formed by shifting and rolling upa graphite sheet. It is known that the end surface of the cylinder of aCNT can be closed by inserting six five-member rings. The fact thatthere are diverse tip end shapes as shown in FIG. 3 is attributable tothe fact that five-member rings can be arranged in various ways. FIG. 4shows one example of the tip end structure of a carbon nanotube; it isseen that this structure varies from a flat plane to a curved surface asa result of six-member rings being arranged around a five-member ring,and that the tip end has a closed structure. Circles indicate carbonatoms, solid lines indicate the front side, and dotted lines indicatethe back side. Since there are various possible arrangements offive-member rings, the tip end structures show diversity.

[0071] Not only carbon nanotubes, but also general nanotubes show such atube structure. Accordingly, nanotubes show an extremely strong rigidityin the central axial direction and in the bending direction; and at thesame time, like other carbon allotropes, etc., nanotubes show extremechemical and thermal stability. Accordingly, when nanotubes are used asprobe needles, these nanotubes tend not to be damaged even if theycollide with atomic projections on the sample surface during scanning.Furthermore, since the cross-sectional diameters of nanotubes aredistributed over a range of approximately 1 nm to several tens ofnanometers (as described above), such nanotubes are most suitable asmaterials of probe needles which can produce sharp images of finestructures at the atomic level (if a nanotube with a small curvatureradius is selected). Furthermore, since there are many nanotubes thathave conductivity, nanotubes can be utilized not only as AFM probeneedles, but also as STM probe needles. Furthermore, since nanotubes aredifficult to break, they can also be used as probe needles in otherscanning probe microscopes such as leveling force microscopes, etc.

[0072] Among nanotubes, carbon nanotubes are especially easy tomanufacture, and are suited to inexpensive mass production. It is knownthat carbon nanotubes are produced in the cathodic deposit of an arcdischarge. Furthermore, such carbon nanotubes are generally multi-layertubes. Furthermore, it has been found that single-layer carbon nanotubesare obtained when the arc discharge method is modified and a catalyticmetal is mixed with the anode. Besides the arc discharge method, carbonnanotubes can also be synthesized by CVD using fine particles of acatalytic metal such as nickel or cobalt, etc., as a substrate material.Furthermore, it is also known that single-layer carbon nanotubes can besynthesized by irradiating graphite containing a catalytic metal withhigh-output laser light at a high temperature. Furthermore, it has alsobeen found that such carbon nanotubes include nanotubes that envelop ametal.

[0073] Moreover, as described above, it has been found that BCN typenanotubes and BN type nanotubes, etc., can also be inexpensivelymanufactured using an arc discharge process or crucible heating process,etc., and techniques for enveloping metals in nanotubes are also beingdeveloped.

[0074] However, for example, in the carbon nanotube manufacturingprocess, it is known that carbon nanotubes are not produced just bythemselves; instead, such nanotubes are produced in a mixture with largequantities of carbon nanoparticles (hereafter also abbreviated to “CP”).Accordingly, the recovery of CNT from this mixture at a high density isa prerequisite for the present invention.

[0075] In regard to this point, the present inventors have alreadyprovided a CNT purification method and purification apparatus based onan electrophoretic process in Japanese Patent Application No. 10-280431.In this method, CNTs can be purified by dispersing the carbon mixture inan electrophoretic solution, and applying a DC voltage or AC voltage.For example, if a DC voltage is applied, the CNTs are arranged instraight rows on the cathode. If an AC voltage is applied, the CNTs arearranged in straight rows on the cathode and anode as a result of theformation of a non-uniform electric field. Since the degree ofelectrophoresis of CPs is smaller than that of CNTs, CNTs can bepurified by means of an electrophoretic process utilizing thisdifference.

[0076] It has been confirmed that this electrophoretic method can beused to purify not only carbon nanotubes, but also BCN type nanotubesand BN type nanotubes.

[0077] This electrophoretic method is also used in the working of thepresent invention. Specifically, nanotubes purified and recovered by theabove-described method are dispersed in a separate clean electrophoreticsolution. When metal plates such as knife edges, etc., are positionedfacing each other as electrodes in this solution, and a DC voltage isapplied to these electrodes, nanotubes adhere to the cathode (forexample) in a perpendicular configuration. If the electrodes arepositioned so that a non-uniform electric field is formed in cases wherean AC voltage is applied, nanotubes will adhere to both electrodes in aperpendicular configuration. These electrodes with adhering nanotubesare utilized in the manufacturing process of the present invention. Ofcourse, other methods of causing nanotubes to adhere to aknife-edge-form metal plate may also be used.

[0078] The above-described electrophoretic solution may be any solutionthat is capable of dispersing the nanotubes so that the nanotubesundergo electrophoresis. Specifically, the solvent used is a dispersingliquid, and is at the same time an electrophoretic liquid. Solventswhich can be used in this case include aqueous solvents, organicsolvents and mixed solvents consisting of both types of solvents. Forexample, universally known solvents such as water, acidic solutions,alkaline solutions, alcohol, ethers, petroleum ethers, benzene, ethylacetate and chloroform, etc., may be used. More concretely, all-purposeorganic solvents such as isopropyl alcohol (IPA), ethyl alcohol, acetoneand toluene, etc., may be utilized. For example, in the case of IPA,carboxyl groups are present as electrophoretic ion species. Thus, it isadvisable to select the solvent used on the basis of a comprehensiveevaluation of the electrophoretic performance and dispersion performanceof the nanotubes, the stability of the dispersion, and safety, etc.

[0079]FIG. 5 shows a case involving CNTs as one example of a DCelectrophoretic process. The electrophoretic solution 20 in which theCNTs are dispersed is held inside a hole formed in a glass substrate 21.Knife edges 22 and 23 are positioned facing each other in the solution,and a DC power supply 18 is applied. Although not visible to the nakedeye, countless extremely small carbon nanotubes (CNTs) are present inthe electrophoretic solution. These CNTs adhere in a perpendicularconfiguration to the tip end edge 22 a of the cathode knife edge 22.This can be confirmed under an electron microscope. In this apparatus, anon-uniform electric field in which the lines of electric force are bentin the direction perpendicular to the plane of the knife edges is formedbetween the two electrodes. However, this can be utilized as a DCelectrophoresis apparatus even if a uniform electric field is formed.The reason for this is as follows: specifically, in the case of anon-uniform electric field, the rate of electrophoresis is merelynon-uniform; electrophoresis is still possible.

[0080]FIG. 6 shows a case involving CNTs as one example of an ACelectrophoretic process. The electrophoretic solution 20 in which theCNTs are dispersed is held inside a hole formed in a glass substrate 21.Knife edges 22 and 23 are positioned facing each other in the solution,and an AC power supply 19 is applied via an amplifier 26. A non-uniformelectric field similar to that of FIG. 5 acts between the electrodes.Even if a non-uniform electric field is not intentionally constructed,local non-uniform electric fields are actually formed, so thatelectrophoresis can be realized. In this figure, a 5 MHz, 90 Valternating current is applied. CNTs adhere in a perpendicularconfiguration to the tip end edges 22 a and 23 a of the knife edges ofboth electrodes.

[0081]FIG. 7 is a schematic diagram showing states of adhesion ofnanotubes 24 to the tip end edge 23 a of a knife edge 23. The nanotubes24 adhere to the tip end edge 23 a in a more or less perpendicularconfiguration, but some of the nanotubes are inclined. Furthermore,there are also cases in which a plurality of nanotubes are gatheredtogether so that they adhere in the form of bundles; these are referredto as NT bundles 25 (also called nanotube bundles). The curvature radiiof the nanotubes are distributed over a range of approximately 1 nm toseveral tens of nanometers. In cases where excessively slender nanotubesare selected as probe needles, such probe needles offer the advantage ofallowing fine observation of indentations and projections in the atomicsurface; conversely, however, such nanotubes may begin to vibrate in acharacteristic mode, and in such cases, the resolution drops. Here, ifan NT bundle 25 is used as a probe needle, the nanotube that protrudesthe furthest forward in this bundle fulfils the function of a directprobe needle, while the other nanotubes act to suppress vibration.Accordingly, such NT bundles 25 can also be used as probe needles.

[0082]FIG. 8 is a computer image of a scanning electron microscope imageof a knife edge with an adhering CNT. It is seen that CNTs can easily becaused to adhere to a knife edge merely by performing an electrophoreticoperation. However, CNTs more commonly adhere to the tip end edge at aninclination rather than at right angles.

[0083] The knife edge shown in FIG. 8 is subjected to a specialtreatment for the purpose of a strength test. This electron-microscopicapparatus contains considerable quantities of organic substances asimpurities. Accordingly, it was found that when this knife edge isirradiated with an electron beam, a carbon film originating in theimpurities is formed on the surface of the knife edge. The details ofthis phenomenon will be described later; however, this carbon film isformed on the knife edge surface so that it covers only some of theCNTs. In other words, the carbon film has the function of fastening CNTsto the knife edge that were merely adhering to the knife edge. Othernanotubes besides CNTs can be similarly treated.

[0084] The mechanical strength of CNTs on the above-described knife edgewas tested. The CNTs were pressed by a member with a sharpened tip.FIGS. 9 and 10 show computer images of scanning electron microscopeimages obtained before and after pressing. As is clearly seen from FIG.10, the CNT has a bending elasticity which is such that there is nobreakage of the CNT even when the CNT is bent into a semicircular shape.When pressing was stopped, the CNT returned to the state shown in FIG.9. Such a high strength and high elasticity are the reason why CNTs arenot damaged even if they contact the atomic surface or are draggedacross the atomic surface. This also verifies that the carbon filmstrongly fastens the CNTs in place. Thus, the fastening force issufficient so that the CNTs are not separated from the knife edge evenif bent. General nanotubes also have such a high strength and highelasticity; this is a major advantage of using nanotubes as probeneedles.

[0085]FIG. 11 is a diagram of a device used to transfer a nanotube tothe cantilever of an AFM holder. A holder 2 a is caused to protrude inthe form of a pyramid from the tip end of a cantilever 2 b. This is amember made of silicon which is manufactured using a semiconductorplanar technique. Ordinarily, such a pyramid-form protruding part isused as an AFM. However, in the present invention, this pyramid-formprotruding part is converted to use as a holder 2 a. A nanotube 24 onthe knife edge 23 is transferred to this holder 2 a, and this nanotube24 is used as a probe needle. Since the nanotubes on the knife edge aremerely adhering to the knife edge, they are naturally not fastened by afilm. These operations are preformed under real-time observation insidea scanning electron microscope chamber 27. The cantilever 2 b can bemoved three-dimensionally in the X, Y and Z directions, and the knifeedge can be move two-dimensionally in the X and Y directions.Accordingly, extremely minute operations are possible.

[0086] The surface signal operating probe of the present invention iscompleted by transferring a nanotube adhering to the knife edge to aholder, and fastening this nanotube to the holder by a fastening means.In regard to this fastening means, two methods are used in the presentinvention. One is a coating film; in this case, the nanotube is fastenedto the holder by means of a coating film. The second method uses afusion-welded part; in this case, the nanotube is caused to adhere tothe holder, and the contact portion is fused so that the two members arebonded to each other. Since nanotubes are extremely slender, the entirebase end portion of the nanotube in contact with the holder tends toform the fusion-welded part. Fusion welding methods include fusionwelding by means of an electric current and fusion welding by electronbeam irradiation.

[0087] Below, concrete examples of nanotube fastening means will bedescribed as embodiments.

[0088] Embodiment 1

[0089] [AFM Probe Fastened by a Coating Film]

[0090]FIG. 12 is a layout diagram showing the state immediately prior tothe transfer of the nanotube. While being observed under an electronmicroscope, the tip end of the holder 2 a is caused to approach veryclose to the nanotube 24. The holder 2 a is positioned so that thenanotube 24 is divided into a tip end portion length L and base endportion length B by the tip end of the holder 2 a. Furthermore, atransfer DC power supply 28 is provided in order to promote thistransfer, and the cantilever 2 b is set on the cathode side. However,the polarity of the DC power supply also depends on the material of thenanotube; accordingly, the polarity is adjusted to the direction thatpromotes transfer. The transfer of the nanotube is promoted when thisvoltage is applied. A voltage of several volts to several tens of voltsis sufficient. This voltage can be varied according to the transferconditions. Furthermore, this power supply 28 may also be omitted. Whenthe approach distance D becomes closer than a specified distance, anattractive force acts on both members, so that the nanotube 24spontaneously jumps to the holder 2 a. As the approach distance Dbecomes closer, the actual values of the lengths L and B approach thepreset design values. This transfer may include cases in which thenanotube 24 contacts both the knife edge 23 and holder 2 a; and thesemay be separated following the formation of the coating film.

[0091]FIG. 13 is a layout diagram showing the state in which thenanotube 24 adheres to the holder 2 a. The tip end portion 24 aprotrudes by the tip end portion length L, and the base end portion 24 badheres to the holder 2 a by the base end portion length B. The tip endportion 24 a constitutes the probe needle. It would also be possible tocause an NT bundle 25 to adhere to the holder instead of a singlenanotube 24. Furthermore, if single nanotubes 24 are transferred andcaused to adhere to the holder a number of times, an effect which is thesame as causing an NT bundle 25 to adhere to the holder can be obtained.In cases where nanotubes are caused to adhere a number of times, theindividual nanotubes can be caused to adhere after being arbitrarilyadjusted. Accordingly, a stable, high-resolution probe can bemanufactured in which the nanotube that protrudes furthest to the frontacts as the probe needle, while the surrounding nanotubes suppressresonance of the probe needle as a whole.

[0092] Next, a coating film is formed over a specified region includingthe base end portion 24 b of the nanotube 24, so that the nanotube 24 isfirmly fastened to the holder 2 a. As seen from FIG. 14, the coatingfilm 29 is formed so that it covers the base end portion 24 a fromabove. As a result of this coating film 29, even if the tip end portion24 a constituting the probe needle should catch on an atomic projection,the probe needle will merely flex into a bent state as described above.Thus, damage such as breakage of the probe needle or removal of theprobe needle from the holder 2 a can be prevented. If this coating film29 is absent, the nanotube 24 will separate from the holder 2 a when thetip end portion 24 a catches on a projection.

[0093] Next, methods which can be used to form the coating film 29 willbe described. As described above, one method which can be used is asfollows: specifically, when the base end portion 24 b is irradiated withan electron beam, carbon substances floating inside the electronmicroscope chamber 27 are deposited in the vicinity of the base endportion so that a carbon film is formed. This carbon film is used as acoating film. A second method is a method in which a very small amountof a reactive coating gas is introduced into the electron microscopechamber 27, and this gas is decomposed by means of an electron beam, sothat a coating film of the desired substance is formed. In addition,general coating methods can also be employed. For example, CVD (alsoreferred to as chemical vapor deposition) and PVD (also referred to asphysical vapor deposition) can be utilized. In the case of a CVDprocess, the material is heated beforehand, and a reactive coating gasis caused to flow to this location, so that a coating film is reactivelygrown on the surface of the material. Furthermore, the low-temperatureplasma method in which the reaction gas is converted into a plasma and acoating film is formed on the surface of the material is also one typeof CVD method. Meanwhile, PVD methods include several types of methodsranging from simple vapor deposition methods to ion plating methods andsputtering methods, etc. These methods can be selectively used in thepresent invention, and can be widely used on coating film materialsranging from insulating materials to conductive materials in accordancewith the application involved.

[0094]FIG. 15 is a scanning electron microscope image of a completedprobe. It is seen that a CNT is fastened to the holder in accordancewith the design. The present inventors took AFM images ofdeoxyribonucleic acid (DNA) in order to measure the resolution andstability of this probe. FIG. 16 shows an AFM image of this DNA; and thecrossing and twining of the DNA were clearly imaged. To the bestknowledge of the inventors, this is the first time that such clear DNAimages have been obtained. Judging from FIG. 16, it appears that the tipend curvature radius of this probe constructed according to the presentinvention is 1.2 nm or less; it will be understood that this isextremely effective in scientific research.

[0095] Embodiment 2

[0096] [Reinforced AFM Probe Fastened by Coating Film]

[0097]FIG. 17 shows another coating film formation method. In order toobtain high-resolution images, it is desirable that the curvature radiusof the tip end of the nanotube 24 be small. However, as described above,there are cases in which the tip end portion undergoes microscopicvibrations if the nanotube is too slender, so that the images becomeblurred. Accordingly, in cases where a slender nanotube 24 is used, acoating film 30 is also formed on a region of the tip end portion 24 athat is close to the base end portion 24 b, i.e., on an intermediateportion 24 c. As a result of this coating film 30, the intermediateportion 24 c is made thicker and greater in diameter, so that an effectthat suppresses microscopic vibrations is obtained. This coating film 30may be formed from the same material as the coating film 29 at the sametime that the coating film 29 is formed, or may be formed from adifferent material. In this way, a probe needle comprising a singlenanotube in which the tip end of the nanotube 24 is slender and the rootof the nanotube is thick can be constructed. In other words, ahigh-resolution, high-reliability probe needle can be constructed from aslender nanotube, without using an NT bundle 25.

[0098] Embodiment 3

[0099] [STM Probe Fastened by Coating Film]

[0100]FIG. 18 is a perspective view of the essential parts of a scanningtunnel microscope probe 2. The tip end portion 24 a of a nanotube 24 iscaused to protrude, and this portion constitutes the probe needle. Thebase end portion 24 b is fastened to a holder 2 a by means of a coatingfilm 29. This probe may be easily understood by a comparison with theprobe 2 in FIG. 1. The actions and effects of this probe are similar tothose of Embodiment 1; accordingly, a detailed description is omitted.

[0101] Embodiment 4

[0102] [Magnetic Probe Fastened by Coating Film]

[0103] A probe similar to that shown in FIG. 18 can be utilized as aninput-output probe in a magnetic disk drive. In this case, iron atomsare embedded in the tip end of the nanotube, so that the nanotube isendowed with a magnetic effect. Since a nanotube has a tubularstructure, various types of atoms can be contained inside the tube.Among these atoms, magnetic atoms can be contained in the tube, so thatthe nanotube is endowed with magnetic sensitivity. Of course,ferromagnetic atoms other than iron atoms may also be used. Since thetip end curvature radius of a nanotube is extremely small, i.e., a valueranging from approximately 1 nm to several tens of nanometers, the inputand output of data recorded at a high density in an extremely smallspace can be performed with high precision.

[0104] Embodiment 5

[0105] [AFM Probe Fastened by Electric Current Fusion Welding]

[0106]FIGS. 19 through 24 illustrate an embodiment of fusion-weldingfastening of the nanotube. First, FIG. 19 is a layout diagram of thestate immediately prior to fusion welding of the nanotube. The tip endof the holder 2 a is caused to approach very closely to the nanotube 24while being observed under an electron microscope. The holder 2 a ispositioned so that the nanotube 24 is divided into a tip end portionlength L and base end portion length B by the tip end of the holder 2 a.Furthermore, a high resistance R, a DC power supply 28 and a switch SWare connected between the knife edge 23 and cantilever 2 b. For example,the resistance value of the high resistance R is 200 MQ, and the voltageof the DC power supply is 1 to 100 V. In FIG. 19, in which the membersare in a close proximity, the switch SW is in an open state, and nocurrent has yet been caused to flow.

[0107] When the two members are caused to approach each other even moreclosely so that the nanotube 24 contacts the holder 2 a, the state shownin FIG. 20 results. Here, the tip end portion 24 a protrudes by anamount equal to the tip end portion length L, and the base end portion24 b adheres to the holder 2 a for a length equal to the base endportion length B. When the switch SW is closed so that current flows inthis stage, current flows between the nanotube 24 and the holder 2 a, sothat the base end portion 24b that is in contact with the holder 2 a isfusion-welded to the holder 2 a by current heating. In other words, thebase end portion 24 b is fused to form the fusion-welded part 24 dindicated by a black color in the figure, and the nanotube 24 is firmlyfastened to the holder 2 a.

[0108] It is also possible to use a process in which the switch SW isclosed prior to the contact between the nanotube 24 and the holder 2 a,after which the base end portion 24 b is converted into thefusion-welded part 24 d by the flow of current caused by contact, andthen the holder 2 a is moved away from the knife edge 23.

[0109] In this electric current fusion welding treatment, not only isthe fastening strong, but fusion welding can be reliably performed withthe feeling of spot welding while confirming the object in the electronmicroscope, so that the product yield is increased. The DC power supply28 may be replaced by an AC power supply or pulsed power supply. In thecase of a DC power supply, fusion welding can be performed using acurrent of 10⁻¹⁰ to 10⁻⁶ (ampere-seconds (A·s)). For example, in a casewhere the diameter of the carbon nanotube (CNT) is 10 nm, and the lengthB of the base end portion is 200 nm, stable fusion welding can beperformed at 10⁻⁹ to 10⁻⁷ (A·s). However, the gist of the presentinvention lies in the fastening of the CNT by fusion welding, and thepresent invention is not limited to these numerical values.

[0110] Embodiment 6

[0111] [AFM Probe Fastened by Electron Beam Fusion Welding]

[0112] The second fusion welding method is the electron beam irradiationmethod. When the switch SW is closed in the non-contact state shown inFIG. 19, an electric field is formed between the holder 2 a and thenanotube 24. When the respective members are caused to approach eachother even more closely, the nanotube 24 is caused to fly onto theholder 2 a by the force of this electric field. Afterward, when all orpart of the base end portion 24 b of the nanotube 24 is irradiated withan electron beam, the base end portion 24 b melts and is fusion-weldedto the holder 2 a as the fusion-welded part 24 d.

[0113] In this case, the polarity of the DC power supply 28 depends onthe material of the nanotube, etc. Thus, this polarity is not limited tothe arrangement shown in the drawings; and the polarity is adjusted tothe direction that promotes transfer.

[0114] An electric field transfer method is used in the above-describedmethod; however, it is also possible to perform a non-electric-fieldtransfer with the switch SW open. Specifically, when the holder 2 a iscaused to approach the nanotube 24 within a certain distance, a van derWaals attractive force acts between the two members, and the nanotube 24is caused to fly onto the holder 2 a by this attractive force. Thesurface of the holder 2 a may be coated with an adhesive agent such asan acrylic type adhesive agent, etc., in order to facilitate thistransfer. Following this transfer, the base end portion 24 b adhering tothe holder 2 a is fused by irradiation with an electron beam, so thatthe nanotube 24 is fastened to the holder 2 a via a fusion-welded part24 d. Thus, a probe similar to that obtained by current fusion weldingcan also be obtained by electron beam fusion welding.

[0115]FIG. 21 is a schematic diagram of the completed probe followingfusion welding. The tip end portion 24 a constitutes the nanotube probeneedle and can be used as a high-resolution probe with a tip endcurvature radius of 10 nm or less. The nanotube 24 is firmly fastened tothe holder 2 a by means of the fusion-welded part 24 d, so that thenanotube 24 does not break, bend or come loose even if subjected to aconsiderable impact. In the case of a carbon nanotube, it appears thatthe nanotube structure is destroyed and changed in amorphous carbon inthe fusion-welded part 24 d. If silicon is used as the material of theholder 2 a, it appears that the carbon atoms that have been convertedinto an amorphous substance and the silicon atoms of the holder bond toform silicon carbide, so that the fusion-welded part 24 d assumes asilicon carbide structure. However, detailed structural analysis of thispart has not yet been completed, and this is merely conjecture at thispoint.

[0116] In the case of BCN type nanotubes or BN type nanotubes,structural analysis of the fusion-welded part has not yet beenperformed. However, it has been experimentally confirmed that themembers are strongly bonded by this fusion-welded part.

[0117] As described above, in cases where the holder 2 a is made ofsilicon, the holder 2 a has a certain amount of conductivity since it isa semiconductor. Accordingly, since a voltage can be directly applied,current fusion welding is possible. Of course, the van der Waalstransfer method or electron beam fusion welding method can also be used.However, in cases where the holder 2 a is constructed from an insulatorsuch as silicon nitride, the holder 2 a has no conductivity. In suchcases, therefore, the transfer method using the van der Waals attractiveforce or the electron beam fusion welding method is the optimal method.In cases where the current fusion welding method cannot be applied to aninsulator, the following procedure may be used: An electrode is formedfrom a conductive substance on the surface of the CNT holder 2 a orcantilever 2 b. An electrode film is formed by means of, for instance,metal vapor deposition, etc. A voltage is applied to this film,resulting in that an electric current flows, the fusion weldingphenomenon occurs, and a probe is thus obtained.

[0118] Embodiment 7

[0119] [AFM Probe Fastened by Coating Film and Fusion Welding]

[0120] In cases where a single nanotube 24 is used as a probe needle, ifthe tip end portion 24 a of the nanotube is long and slender, it couldhappen that resonance occurs so that the tip end vibrates, thus causinga drop in resolution. In order to suppress such resonance, there is amethod in which an additional coating film is formed on specifiedregions. As is clear from FIG. 22, if a coating film 30 is formed on theroot side of the tip end portion 24 a, this portion becomes thicker sothat resonance tends not to occur. This coating region can be freelydesigned; accordingly, a coating film 29 which extends to the base endportion 24 b may be formed. This coating film 29 has the effect ofpressing the nanotube from above. Thus, together with the fusion-weldedpart 24 d, the coating film reinforces the fastening of the nanotube 24to the holder 2 a. The thickness of the coating films 29 and 30 may bevaried depending upon the case.

[0121] Next, methods for forming the coating films 29 and 30 will bedescribed. As described above, in one method, when the base end portion24 b and intermediate portion 24 c are irradiated with an electron beam,not only do these portions melt, but carbon substances floating insidethe electron microscope chamber 27 are deposited in the vicinity of thebase end portion so that a carbon film is formed. This carbon film canbe utilized as a coating film. In another method, a trace amount of areactive coating gas is introduced into the electron microscope chamber27, and this gas is broken down by an electron beam, so that a coatingfilm of the desired substance is formed. In addition, general coatingmethods can also be employed. For example, the CVD (also called chemicalvapor deposition) or PVD (also called physical vapor deposition) can besimilarly utilized. Details of these methods are omitted here.

[0122] It is also possible to fusion-weld an NT bundle 25 instead offusion-welding a single nanotube 24. If a plurality of nanotubes 24 arefusion-welded one by one, the same effect as the fusion welding of an NTbundle 25 can be obtained. In cases where such fusion welding isperformed one by one, the individual nanotube can be arbitrarilyadjusted and fusion-welded. Accordingly, a stable, high-resolution probecan be obtained in which a nanotube that protrudes furthest forward actsas the probe needle, while the surrounding nanotubes suppress resonanceof the probe needle as a whole.

[0123] Embodiment 8

[0124] [STM Probe Fastened by Fusion Welding]

[0125]FIG. 23 is a perspective view of the essential portion of ascanning tunnel microscope. The tip end portion 24 a of a nanotube 24 iscaused to protrude, and this portion acts as a probe needle. The baseend portion 24 b forms a fusion-welded part 24 d and is fusion-welded tothe holder 2 a. This probe will be easily understood if compared withthe probe 2 shown in FIG. 1. A metal such as tungsten or aplatinum-iridium alloy, etc. can be used as the material of the holder 2a. The actions and effects of this probe are similar to those ofEmbodiment 5. Accordingly, details thereof are omitted.

[0126] Embodiment 9

[0127] [STM Probe Fastened by Coating Film and Fusion Welding]

[0128]FIG. 24 shows a probe 2 in which a coating film 30 is formed onthe intermediate portion 24 c of the nanotube 24. This coating film 30is installed in order to prevent vibration of the probe needle. As inFIG. 22, a coating film 29 which covers the fusion-welded part 24 d maybe formed. Since the actions and effects of this probe are similar tothose of Embodiment 7, details are omitted.

[0129] Embodiment 10

[0130] [Magnetic Probe Fastened by Fusion Welding]

[0131] A probe similar to that shown in FIG. 23 can be utilized as aninput-output probe for a magnetic disk drive. In this case, iron atomsare embedded in the tip end of the nanotube, so that the nanotube isendowed with a magnetic effect. Since a nanotube has a tubularstructure, various types of atoms can be contained inside the tube. Asone example, ferromagnetic items can be contained in the tube, so thatthe nanotube is endowed with magnetic sensitivity. Of course,ferromagnetic atoms other than iron atoms may also be used. Since thetip end curvature radius of a nanotube is extremely small, i.e.,approximately 1 nm to several tens of nanometers, processing such as theinput and output of data recorded at a high density in a very smallspace, etc. can be performed with high precision.

[0132] The present invention is not limited to the above-describedembodiments; and various modifications and design changes, etc., withinlimits that involve no departure from the technical spirit of thepresent invention are included in the technical scope of the invention.

Industrial Applicability

[0133] As described in detail above, the present invention relates to anelectronic device surface signal operating probe which comprises ananotube, a holder which holds this nanotube, and a fastening meanswhich fastens the base end portion of the nanotube to the surface of theholder in a manner that the tip end portion of the nanotube protrude, sothat the tip end portion of the nanotube is used as a probe needle; andit also relates to a method for manufacturing the same. Since a nanotubeis thus used as a probe needle, the tip end curvature radius is small.Accordingly, by way of using this probe needle in a scanning probemicroscope, high-resolution images of surface atoms can be picked up.When this probe needle is used as the probe needle of a magneticinformation processing device, the input and output of high-densitymagnetic information can be controlled with high precision.

[0134] Since nanotubes have an extremely high rigidity and bendingelasticity, no damage occurs to nanotubes even if they should contactneighboring objects. Accordingly, the useful life of the probe can beextended. Furthermore, carbon nanotubes are present in large quantitiesin the cathodic deposits of arc discharges, and other BCN type nanotubesand BN type nanotubes can easily be manufactured by similar methods.Accordingly, the cost of raw materials is extremely low. In themanufacturing method of the present invention, probes can beinexpensively mass-produced, so that the cost of such probes can belowered, thus stimulating research and economic activity. In particular,STM and AFM probes with a long useful lives that are necessary for thecreation of new substances can be provided inexpensively and in largequantities. Thus, the present invention can contribute to the promotionof technical development.

1. A surface signal operating probe for an electronic devicecharacterized in that said probe comprises a nanotube 24, a holder 2 awhich holds said nanotube 24, and a fastening means which fastens a baseend portion 24 b of said nanotube 24 to a surface of said holder with atip end portion 24 a of said nanotube 24 being caused to protrude; andsaid tip end portion 24 a is used as a probe needle so as to scansurface signals.
 2. The surface signal operating probe according toclaim 1, wherein said fastening means is a coating film 29, and saidnanotube 24 is fastened to said holder 2 a by way of covering aspecified region including said base end portion 24 b of said nanotube24.
 3. The surface signal operating probe according to claim 2, whereina reinforcing coating film 30 is formed on an intermediate portion 24 cof said protruding tip end portion 24 a near said base end portion 24 bof said nanotube
 24. 4. The surface signal operating probe according toclaim 1, wherein said fastening means is a fusion-welded part 24 d, andsaid base end portion 24 b of said nanotube 24 is fastened to saidholder 2 a by fusion welding by means of said fusion-welded part 24 d.5. The surface signal operating probe according to claim 1, wherein aplurality of said nanotubes 24 are bundled to form an NT bundle 25 inwhich one of said nanotubes is caused to protrude furthest forward, andsaid NT bundle 25 is fastened to said holder 2 a as said nanotube
 24. 6.The surface signal operating probe according to claims 1 through 5,wherein said electronic device is a scanning probe microscope, and saidnanotube 24 is used as a probe needle so as to detect physical andchemical actions on a surface of a sample.
 7. The surface signaloperating probe according to claim 6, wherein said holder 2 a is formedfrom a conductive material, and said scanning probe microscope is ascanning tunnel microscope.
 8. The surface signal operating probeaccording to claim 6, wherein said holder 2 a is installed so as toprotrude from a cantilever 2 b, and said scanning probe microscope is anatomic force microscope.
 9. The surface signal operating probe accordingto claims 1 through 5, wherein said electronic device is a magneticinformation processing device, and magnetic information is inputted ontoand outputted from a magnetic recording medium by means of said nanotube24.
 10. The surface signal operating probe according to claims 1 through9, wherein said nanotube is one selected from a group consisting of acarbon nanotube, BCN type nanotube and BN type nanotube.
 11. A methodfor manufacturing a surface signal operating probe for an electronicdevice, said method being characterized in that said method comprises: afirst process in which a voltage is applied across electrodes 22 and 23in an electrophoretic solution 20 in which nanotubes 24 to be used as aprobe needle are dispersed, so that said nanotubes are caused to adhereto said electrodes in a protruding fashion; a second process in whichsaid electrodes to which nanotubes 24 are caused to adhere in aprotruding fashion and a holder 2 a are caused to approach very close toeach other, so that each of said nanotubes 24 is transferred to saidholder 2 a in such a manner that a base end portion 24 b of saidnanotube 24 adheres to a surface of said holder with a tip end portion24 a of said nanotube in a protruding fashion; and a third process inwhich a specified region including at least said base end portion ofsaid nanotube adhering to said surface of said holder is subjected to acoating treatment so that said nanotube 24 is fastened to said holder 2a by a resulting coating film
 29. 12. The surface signal operating probemanufacturing method according to claim 11, wherein in which a voltageis applied across said electrodes and holder when necessary in saidsecond process.
 13. A method for manufacturing a surface signaloperating probe for an electronic device, said method beingcharacterized in that said method comprises: a first process in which avoltage is applied across electrodes 22 and 23 in an electrophoreticsolution 20 in which nanotubes 24 to be used as a probe needle aredispersed, so that said nanotubes are caused to adhere to saidelectrodes in a protruding fashion; a second process in which saidelectrodes to which nanotubes 24 are caused to adhere in a protrudingfashion and a holder 2 a is caused to approach very close to each other,so that each of said nanotubes 24 adheres to a surface of said holderwith a tip end portion 24 a of said nanotube in a protruding fashion;and a third process in which an electric current is caused to flowbetween said nanotube 24 and said holder 2 a so that a base end portion24 a of said nanotube 24 is fusion-welded to said holder 2 a.
 14. Amethod for manufacturing a surface signal operating probe for anelectronic device, said method being characterized in that said methodcomprises: a first process in which a voltage is applied acrosselectrodes 22 and 23 in an electrophoretic solution 20 in whichnanotubes 24 to be used as a probe needle are dispersed, so that saidnanotubes are caused to adhere to said electrodes in a protrudingfashion; a second process in which said electrodes to which nanotubes 24are caused to adhere in a protruding fashion and a holder 2 a is causedto approach very close to each other, so that a nanotube 24 adheres to asurface of said holder with a tip end portion 24 a of said nanotube in aprotruding fashion; and a third process in which a base end portion 24 bof said nanotube 24 is fusion-welded to said holder 2 a by irradiationwith an electron beam.
 15. The surface signal operating probemanufacturing method according to claims 11 through 14, wherein saidsecond and third processes are performed while actually observing saidprocesses under an electron microscope.
 16. The surface signal operatingprobe manufacturing method according to claims 11 through 14, whereinsaid nanotube is an NT bundle 25 comprising a plurality of nanotubes,and said NT bundle is fastened to said holder 2 a so that one of saidnanotubes is caused to protrude furthest forward.
 17. The surface signaloperating probe manufacturing method according to claims 11 through 14,wherein said nanotube 24 is one selected from the group consisting of acarbon nanotube, BCN type nanotube and BN type nanotube.